Q. What Is the RCx MSA?

The RCx MSA (Multi Source Agreement) is developing a specification for a high density, low cost, passive copper connector and cable system specifically designed for Intra-Rack connectivity of 25Gb, 50Gb, and 100Gb Ethernet. RCx stands for Rack Connect x (up to 4 lanes).

Q. RCx, why now? We have SFP+ and QSFP+?

With the explosion of GbE ports in the data center and Top-of-Rack (TOR) topologies be used in the coming years, a simpler less expensive interconnect is needed to address cost, power and configurability.

QSFP28 and SFP28 were created as a general purpose connector and cables systems that supports both passive electrical, active electrical and active optical solutions for a variety of signaling standards and distances. Due to its multipurpose design, the QSFP28 and SFP28 connector and cable systems sacrifices simplicity and low cost in order to support multiple power options (including high powered options), identification EEPROMs, I2C interfaces, etc.

When using QSFP28 connectors on switches, users are forced to use multiple cable types to direct-attach to network adapters with different connector types on them in the same rack. For example, connecting to adapters with SFP28 connectors, users must utilize QSFP28 to quad SFP28 “octopus” breakout cables to provide connectivity. Likewise, if the adapter is using QSFP28 connectors, then a QSFP28 to QSFP28 direct attach cable must be used. With RCx, switches can support the standard RCx4 connector yet can also accommodate RCx1-to-RCx1 direct attach cables (25G), RCx2-to-RCx2 direct attach cables (50G), or RCx4-to-RCx4 direct attach cables (100G). No break-out or “octopus” cables are required unless desired.

Q. Who are the original members?

There are four original members (in alphabetical order): Amphenol, Broadcom, Dell and Hewlett Packard Enterprise.

Q: Does RCx support optical interfaces?

No. RCx is a purpose-built, direct attach copper interface with no provision for power or active devices such as optics.

Q. Is RCx compliant to electrical channel standards?

Yes. RCx supports the 802.3by (25GE) as well as 802.3bj (100GE) channel standards and CEI-56G-PAM4-LR.

Q. Does RCx support an EEPROM for cable identification?

No; however, there are two cable ID pins per physical lane which identify the cable compliance to the appropriate 25GE standards.

Q. What does bifurcatable lanes mean?

A 4-lane RCx4 receptacle can be used as a 4-lane port, or can be bifurcated to be used as multiple 2-lane and 1-lane ports. Similarly, a 2-lane RCx2 receptacle can be used as a 2-lane port, or can be bifurcated to be used as multiple 1-lane ports.

Q. What is the density of RCx?

The RCx is density optimized to accommodate more than 128 25G lanes in 1 RU faceplate. Two RCx2 receptacles can fit on a half-height PCIe card faceplate and two RCx4 receptacles can fit on a full-height PCIe card faceplate.

Q. Where can I purchase RCx Connectors or Cables?

Currently Amphenol is the primary vendor for RCx, but it is anticipated that other vendors will be introduced in due course.

Q. Are between series adapter cables available?

It is anticipated that a full family of between series adapter cables will be available, including RCx terminated with either QSFP or SFP. Both breakout and point-to-point variants will be supported.

Q: What is the maximum cable length supported?

The cable length depends on whether RS-FEC is employed on the PHYs of the switch and adapter. RCx has been design to allow operation at up to 3m without RS-FEC being enabled. With RS-FEC enabled, up to 5m of cable can be supported in accordance with the 802.3 standards.

Q. Does RCx support LEDs?

The RCx connectors and cables have been designed such that the face plates of switches and adapters can accommodate LEDs that are visible even when all connectors are fully populated with cables.